1. Field of the Invention
The present invention relates to a puncture needle assembly provided with a puncture needle hub or a detachable end plug assigned and constructed to permit the flush back of blood during puncture of an artery or the like regardless of the positions of fingers.
2. Description of the Prior Art
When the tip of a puncture needle is correctly positioned in the desired blood vessel, especially an artery, the blood flows back into a transparent or translucent hub of the puncture needle due to the blood pressure through the inner bore of the puncture needle. This phenomenon is generally referred to as "flush back". The confirmation of the fact that the tip of the puncture needle is correctly located in the blood vessel is made through a visual check of the flush back of the blood. If the tip of the puncture needle hub opens, the flushing blood will come out of the puncture needle hub undesirably.
Alternatively, U.S. Pat. No. 3,055,361 discloses a structure wherein a catheter hub and vent plug are provided at both interfaces thereof with at least one mating vent groove, so that alignment of these grooves due to the relative rotation of the catheter hub and the vent plug if required ensures escape of air contained. However, this structure has drawbacks in that after air purge relative turning of the two elements out of alignment of the grooves is required, otherwise the blood would leak out of the grooves. In order to obviate this inconvenience, such a puncture needle assembly has been developed as having a detachable air vent plug which is opened at its end and provided with a membrane filter or the like permeable only to the air and adapted to prevent the blood from passing therethrough, the air vent plug and the puncture needle hub cooperating with each other in defining therebetween a small chamber communicated with the inner bore of the puncture needle. In puncturing a blood vessel, the air in the puncture needle and the small chamber is forced out through the membrane filter while the blood is allowed to flush back into the small chamber. In this puncture needle assembly, the hub has a rectangular parallelopiped shape. In use, the puncture needle is pushed to puncture the tissue and the blood vessel with the puncture needle hub pinched at its opposite side surfaces parallel to the puncture needle by the first finger (thumb) and the second finger (forefinger). This puncture needle assembly is suitable for the puncture of a blood vessel which is comparatively shallow in the tissue, e.g. veins, because in such a case only a small force is required for the puncture. However, with the manner of pinching of the hub stated above, it is quite difficult to correctly puncture a blood vessel which is deep in the tissue, e.g. arteries, because in such a case a large force is required to penetrate the tissue. This difficulty is encountered, for example, when a seldinger needle, which is used for inserting an angiography catheter into an artery or when a puncture needle for securing an artery, is driven into the latter. In such cases, the needle encounters a large resistance due to the elasticity of the artery or the tightness of the tissue. The seldinger needle or the puncture needle consists of two or three members including a catheter, inner needle or a dilator. In puncturing, the inner needle hub is held by a hand and, a catherter hub and the dilator hub are also held so that they may move together with the inner needle. As stated before, the puncturing requires a large force and, hence, is extremely difficult to conduct if the hubs are pinched at opposite side surfaces by the first finger (thumb) and the second finger (forefinger).
To overcome this problem, it has been proposed to provide the catheter hub with two flanges so that the puncture needle assembly may be held by three fingers: namely, the second finger (forefinger) retained on one flange, third finger (middle finger) retained on the other flange and the first finger (thumb) placed on the end of the puncture needle hub. This arrangement of fingers, identical to that in the use an of ordinary syringe, permits a comparatively easy puncture. This proposal, however, cannot be applied to the aforementioned puncture needle assembly in which the hub is opened only at its end, because the opened end is closed completely by the bulb of the thumb to prevent the air in the needle and the small chamber from being relieved. In consequence, the blood cannot flush back into the small chamber so that the correct puncture cannot be confirmed visually. In addition, this type of puncture needle assembly cannot be used in combination with another instrument such as a syringe because of the presence of a filter in the opening of the puncture needle. In consequence, the users have been obliged to use other means.